Many of you will recognize that title from a Duke Ellington standard. When you listen to (or play) this song, “Mood Indigo” seems appropriate, because the layered, sometimes ambiguous, yet highly emotive, progression is deeper and richer than anything that is simply “blue.”
And there’s actually a very strong correlation to the fish and the water when you think about it.
What I mean is, sometimes the tune isn’t obvious, and sometimes it doesn’t jump and roll. I’m talking about those bright, hot summer afternoons when the hatch isn’t happening (no jumping… no rolling). In those situations, it’s often less about tempo than it is about tone. And the best tones (and fly colors) often skew toward the indigo-violet shades of the spectrum.
Why does a purple prince nymph catch trout? After all, you can turn over a million river rocks and you won’t find a single bug that looks anything like a purple prince. But countless anglers swear by this bug, especially in the dog days of summer.
Science will tell you that a couple factors might be at work here. First, we should wonder if the eyes of trout are actually more receptive to blues and purples than they are to reds and oranges. Second, we know that water—specifically light penetration through water—does funny things to colors. Bright red on a fly on the river’s surface, or a foot deep, turns to a dull shade of gray when it’s several feet deeper. Indigo is still indigo at the bottom of a run.
Whether that grabs the trout’s attention, or makes the profile of a nymph fly (or streamer) “pop” better… well I can only guess. I’m no trout, after all. All I know is that I’ve learned to fish blues and purples on those days when it seems like nothing natural is really “busting” and I have to reach deepest in to the bag of tricks to tease a bite. When it’s “on,” well, naturally, every detail matters as you try to replicate bugs, from size to profile, and certainly color. That’s when the muted natural colors matter most. But when you’re simply teasing (some call that “attractor” fishing), you need to think beyond the yellows, greens, and grays, and venture into the blues.
The river—and the fish—will inevitably tell you when it is a “Mood Indigo” day. Tune into that phenomenon, and you’ll catch trout when you might otherwise have simply stopped playing.